Air separation technology has been practiced in the industrial world with the major goals being the isolation of the greatest proportion of air components, such as nitrogen, oxygen and argon, as a given system will allow. During the past decade, as energy has become a larger factor in all industrial processes, the efficiency of any given air separation technique has become of greater significance. Various improved techniques have been developed for efficiently separating air depending upon the particular product volume required and a determination as to whether only a sole product will be recovered or a number of products, such as nitrogen and oxygen, will be recovered. However, a common requirement of most air separation procedures and particularly cryogenic and swing adsorption techniques, has been the requirement that water, hydrocarbons and carbon dioxide be removed from the feed air stream prior to liquefaction or selective adsorption. This latter problem has been handled by the prior art in several ways.
In U.S. Pat. No. 2,944,627 a process for separating gas mixtures is disclosed wherein an object of the patent is to remove water in an initial adsorption bed. The patent discloses that a pulse or wave front of water laden adsorbent occurs in the bed during the adsorption cycle.
In U.S. Pat. No. 3,206,918, the drying of air in switching adsorption beds is set forth, wherein the heat of vacuum pumping during regeneration is supplied to the regenerating bed in order to assist the regeneration. The heat is not retained for subsequent use.
U.S. Pat. No. 3,230,689 describes a method for drying gases in which the heat of adsorption is recovered and is utilized to heat a regeneration gas for the desorption of an adsorption bed which is not on-line. The heated regeneration gas is allowed to exit the feed end of the adsorption bed being regenerated.
In U.S. Pat. No. 3,733,775, a method is set forth for regenerating an adsorption bed by the passage of a heated gas co-current to the feed gas through the regenerating adsorption bed. The beds are subsequently cooled prior to going back on-line.
U.S. Pat. No. 4,093,429 is directed to an adsorption process for gas separation wherein the zones of various adsorbates in the bed and their manner of travel through the bed is set forth.
In U.S. Pat. No. 4,165,972, a gas separation system is set forth wherein a heated regeneration gas is passed through a desorbing bed to assist in the desorption. The heated gas, after exiting the desorbing bed is then cooled in order to be utilized to cool a subsequent bed before that bed goes on-line in the adsorption sequence.
U.S. Pat. No. 4,233,038 discloses a gas separation system in which a water and carbon dioxide adsorption bed is set forth. In regeneration, a heated gas passes countercurrently through the water adsorption zone and then a cooled regeneration gas is passed co-currently through both the heated water adsorption zone and the carbon dioxide adsorption zone. A thermal zone from the heated water adsorption zone is carried through the carbon dioxide adsorption zone in order to regenerate the latter zone. However, the heated gas is then exhausted without conservation.
In U.S. Pat. No. 4,249,915, a process is disclosed for the removal of water and carbon dioxide prior to an air separation process, wherein the water is removed in a pressure swing cycle and the carbon dioxide is removed in a temperature swing cycle.
U.S. Pat. No. 4,324,566 discloses an adsorption scheme for the separation of gas components wherein the adsorption is performed with a variable temperature feed gas which varies between a predetermined high temperature and a predetermined low temperature in order to perform a selective adsorption. The prior art attempts to perform the removal of carbon dioxide from a gas stream preparatory to the further separation of the gas stream have various drawbacks relating to the energy efficiency of the adsorption and most particularly the regeneration of the adsorption beds utilized in removing carbon dioxide from the feed gas stream. The prior art generally fails to conserve the heat utilized for a particular bed regeneration and requires a cooling sequence in order to return a regenerated bed to on-line conditions. These drawbacks require additional energy input, which input is unnecessary with the improvements of the present invention as set forth below.